Traffic control system



Jan. 30, 1940. G..w. THOMPSON ET AL 2,188,731

TRFFIl-C CONTROL SYSTEM Filed March 24, 1957 3 Sheets-Sheet 1 /NVENTORS Lmeopencvb uLevDsNsHAw B Y sonee WILLIAM'HoMPsgN dwacmg/w ATTORNEY Jan 30, 1940- G. w. THOMPSON ET Al. 2,188,731

TRAFFIC CONTROL SYSTEM Filed March 24, 1957 3 Sheets-Sheet 2 ALFQED Dencv Dmv QsNsuAw B y 650265 WILLIAM THoMsoN A TT ORNE Y Jan 30, 1940- G. w. THOMPSON ET AL. 2,188,731`

TRAFFIC CONTROL SYSTEM Filed March 24, 1937 5 Sheets-Sheet 3 .1J/5mm- Fly' /fv fffr wf i ZZ- l Z-Jooo e I Z1 wfsroz/A/U j @45mm/ND y2- Y-2000 A (A7055 M l my @055 6 \f I APP/904mm X fvwm/W T/ME /N SECO/V05 ATTORNEY.

Patented Jan. 30, 1940 l UNITED `sTaTlais TRAFFIC CONTROL SYSTEM George William Thompson, Liverpool, and Alfred Percy Bailey Renshaw, yKingston Hill, England, assignors to Automatic Telephone & Electric Company, Limited, London, England, aritish company Application March 24, 1937, Serial No. 132,666 In Great Britain March 30, 1936 15 Claims.

The present invention relates to traffic control signals for use at road crossings or the like and is more particularly concerned with trafiic control systems of the progressive type by means c of which a number of controllers located at successive intersections on a main road may be regulated in al certain phase relationship to each other so that if the average speed of the tran-lc is known it is possible to arrange the signals so l that main road 'traino passing the first intersection willfnot be held up-at succeeding intersections. The invention moreover is particularly concerned with systems in which under light trafc conditions the operation of the 'signals may l be controlledI in accordance with thedensity of the trahie by the employment of vehicle detectors located in the roadway. I

Arrangements have already been suggested in which, while traflic is light, the signals at each intersection are controlled in accordance with the traffic thereatl without relationship to the traflc at other intersections, but in which when the traffic on the main road becomes so heavy as to be substantially continuous, that is to say 2 5 the controllers become in effect fixed time controllers working on their maximum timing limits, the timing of the signals is automatically brought under control of a master controller which thereupon imposes a rigidplan according to which the signals are operated in a related sequence so as to ensure that the traffic on the main road shall'be subject to ka minimum amount of delay when passing through the series of intersections. For example the phase relationship between the signals at two adjacent intersections may conveniently be such that the main road is opened at one of the intersections a predetermined interval before it is opened at the other intersection which interval is suiacient for a vehicle trav- 40 elling at a predetermined speed to travel from one intersection to the other.

In the form of such a system disclosed in British Patent No. 403,732, and the corresponding convention Patent 2,129,446, a master timer is employed from which separate pairs of conductors radiate to the controllers at each intersection for the purpose of regulating their time periods in relation to one another. In the case of continuous main lroad traffic with traiiic wait- 13) ing on the cross roads, even though the maximum timing condenser in any controller becomes fully charged it is impossible for it to discharge through the associated neon lamp and change the rightof-way until a pulse is received from the master timer. Thus when the maximum time limit is reached the signals will not immediately change but rather the circuit will be put into a condition'such as to be responsive to the regulating pulses from the master timer. In practice in y an installation of this type it has been found t3 necessary to reduce the main road maximum period of each controller so that'the mainroad will not become congested before the master vcoritroller pulses become effective and with this arrangementthe traffic can more easily come into c line with the predetermined progressive plan. Unfortunately however during light trafficA conditions there will be a correspondingly'greater possibilityof a controller at any one intersection reaching the maximum time limit dueto a small le block of traffic and therefore being responsive to a possible pulse from the master controller which would inthis case cause unnecessary interference. Furthermore during periods of substantially'continuous traflic the arbitrary termination of-'right- 2c of-way 'periods by vthe master controller takes no account of the traino conditions at any particularfmoment and proves iniiexible and somewhat expensive' in practice and the chief object of' the present invention is to effect an improve- 25 ment in the operation in this respect.

According to the invention in a traiiic control system employing a plurality of sets of signals located at v adjacent intersections, interlinkin'g circuits are provided between successive con- 30 trollers which enablethe maximum timing arrangements at each to'be started in operation progressively, the necessary displacement of the start signals being secured by an additional timer in each individual controller. 35

The invention will be better understood from the following description of one method' of kcarrying it into effect, reference being had to the accompanying drawings comprising Figs. 1 to 4. Fig. 1 shows the equipment of an individual con- 40 troller, part of which is shown separately in Fig. 2. Fig. 2 also shows-typical arrangements of interlinking between three successive controllers associated with intersections designated X, Y, and Z which are shown in diagrammatic form vin Fig. 3. Fig. 4 shows the effect of interlinking in' Y a time distance diagram of progressive traflic movement through the three intersections, X. Y, and Z.

It should be explained generally that the controller illustrated in Fig.. 1 is of the type now well-known, and shown in the British patent previously referred to in which a number of contact springs are operated by a'cam shaft which is rotated step by step by means of a solenoid. The

solenoid is operated at suitable intervals which are determined by the time taken to charge a condenser through a high resistance until it attains the striking voltage of a neon or similar gas discharge tube whereupon the tube hashes and a relayin series therewith is operated to bring about the advance of the cam shaft to the l next position.

The controller shown makes use of the usual arrangement of two timing circuits one of which is controlled from the vehicle detectors so that if traftc continues to arrive on the road possessing right of way the condenser is intermittently discharged and thus an extension of the right of way period is obtained. In order however that one road may not hold right of way indefinitely if traiiic is waiting on the other road, the second vtiming circuit is provided and in this the condenser is charged steadily and cannot be discharged by further operations of the detector. Consequently if a detector has been operated in the blocked road this second timing circuit sets a maximum value to the period which a vehicle thereon will have to wait. In the arrangement illustrated the improved working according to the invention is obtained by the provision of a third timing circuit which is set into operation on reception of a call extended during the main road red-amber period of the preceding intersection to indicate that traflic is about to be released from that intersection. This timing circuit functions to measure olf a time approximating that required for vehicles to traverse the distance between the two intersections and when it completes timing this predetermined interval, ay circuit is completed to commence timing the maximum period in order that the released block of traiic may proceed without interference to the intersection ahead where the process is repeated. It may be arranged that unless the signals at the 'called intersection are giving right of way to the main road the linking pulse from the calling intersection is lost, or alternatively, that the pulse is stored no matter what the Signal indication is at the time of reception of the pulse; the relative merits of the two arrangements will be more fully appreciated from the ensuing detailed description.

Considering now the detailed operation of the circuit, it is assumed that the controller is fed from alternating current mains connected to the transformer TR which is conveniently provided with suitable tapping points to suit different ymains voltages. From the outer secondary windings of this transformer the valve rectifier VR is fed and this sup-plies direct current to the terminals marked plus and minus, suitable smoothing devices being employed, From the terminals L and Q of the inner secondary winding alternating current at a low voltage is obtainable for use in the vehicle detector circuit. Normally one conductor of the mains will be connected to earth and the terminals concerned are indicated by a minus sign in a circle and square. The terminals marked T are provided for convenience in testing. f

The table at the right hand side of Fig. 1 shows `by heavy black dots and bars the shaft positions in which the various cam contacts are closed. It will be understood that in the absence of traffic the shaft will be standing in either position 3 or position 6 corresponding to the so-called vehicle interval position for either phase B or phase A respectively, the latter being associated with main road traffic and the former with cross road traic.

Referring now to Figs. 2 and 3, Fig. 3 shows a main road in diagrammatic form while Fig. 2

shows the method of interlinking between the Y controllersat the intersections X, Y and Z. In

the arrangement shown it will be assumed that there is a clear stretch of main road leading'inwards towards the intersections X and Z and interlinking therefore will only be required between X, Y and Z. In addition to the interlinking of the controllers so that the maximum timing circuits .e of each successive controller can be started up progressively, facilities for repeated detector impulsing are also provided on the lines disclosed in British Patent 446,288, andthe corresponding convention Patent 2,145,031. It will be understood that the controllers at each intersection are supstantially identical, certain interlinking equipment however not being required at the outer intersections X and Z.

Referring now to Figs. l and 2, it will be assumed that the diagram comprisingFig. l when arranged in conjunction withythe portion of Figure 2 between the center pair of dotted lines represents the controller `at intersectionY andk that the cam shaft is standing in position Sjgiving right of Way to cross road `traiiic or yphase B. Traffic arriving on the cross road will intermittently operate the detector DB, Fig. Land hence y relay D, and this relay at armature-d2 will shunt the condenser QA over resistancevYC since cam` contacts CIG are closed. `The charging circuit for condenser QA extends from positive over cam contacts CIE vand the phase` B vehicle interval adjusting switch VB which is suitably wired to the tappings of the common resistance AR.

Assuming now that a vehicle operates phase A detector yl or y2, Fig. 3, relays O' vor P, Fig. 2 l

If now a break occurs in the phase B trafiic of suflicient length to permit the striking voltage of the neon lampi FA to'be reached `orfshould the maximum condenser QB vbe charged to the striking voltage of the neon lamp FB, either relay A or relay B `will be operated to energize the solenoid S which in turn will advance the cam shaft to position 4. The solenoid contacts SI and S2 operate momentarily todischarge condensers QA and QB by way of the resistances YAand YB respectively so as to ensure that they start the next timing period with no residual charge. In position 4 cam contacts C2- are closed and the charging circuit for condenser QA therefore .extends over the phase B amber adjusting switch LB. If the stepping of the" cam shaft has been brought about by relay B due to a change on maximum, armature b2 and cam contacts S4 will have ensured that relay D still remains ,energized and consequently, with contacts d4 open the charging circuit will now include resistance YD which gives an extended amber period to give time for cross traiiic to clear the intersection. The continued energization of relay D ensures that right of way shall return to phase B without any further detector operation so' as to release any vehicles which mayhave been stopped after however, resistance YD is short circuited by con? tacts d4 and the amber period is correspondingly shortened. It willloe appreciated that some `degrec of extension of the period is obtained if the detector DB is crossed by a Vehicle during the amber period. v

When the cam shaft advances to position 5 after the expiration ofr the amber period,`

charging of the condenser 2A takes place over cam contactsCS and the phase A initial interval adjusting switch IA and'at the end of the period determined thereby, the cam shaft steps to position 6. The length of the initial interval cannot be affected by the operation of either of the 'detectors. The cam shaft is now in the vehicle interval position -for phase A and the locking circuit for relay E will be opened at cam contacts CI2. Phase A traiiic will now intermittently operate relaiT E and if there are any waiting vehicles on phase B relay D willy be operated and locked up by way of cam contacts CI and contacts di. Charging circuits will thereupon be .completed for condenser QA over cam contacts C4 Aby way ofv the phase A vehicle interval switch VA and for condenser QB by way of 'cam contacts CIB, armatures d3 and m2 and the entire resista-nce BR'. Should the density of the traino be suoli as to prevent condenser QA from charging suiiiciently, the changeover of the signals will be dependent on the maximum timing condenser QB but since the whole of resistance BR is included in the maximum timing circuit, the maximum. period will be' exceedingly long. Normally however the operation of-relay M will at armature m2 connect the ordinary maximum adjustswitch MA in circuit as will be described .subsequently.

Itwill be understood that the signalling lamps GA. AB, RB, GB, AA and RA are operated over cam contacts C9, CH3, CII, C20, C2i and C?? respectively in a manner which will be readily followed from the cam contact operation table.

The strap between the amber lamps AAv and is employed to give an amber indication to both phases immediately prior to the change to green.

The switches lPA and PB associated with the detector circuits are soi-called .arterial switches and the closing of one of these switches will ensure that right of way will return to the asso-- ciated phase in the absence of traic on the other' phase. The effect of these switches is to nut in a call but not to produce any extension in the` absence of traffic. The manual control terminal MC may be connected via a push button toenm able stepping of the solenoid to be eiected uallv.

Referring now to Figs. 2 and 3 it will be assuroerl that the controllers at intersections X. Y and all of which are similar to that for intersection Y shown Figjl rand part of Fig. 2, are all operating individually under light traiiic conditions and that the controller'at intersection shows red to main road.l i. e., the shaft is in position 3. Assume now that a block of traffic approaches intersection X along the main .in the direction left to right and thereupon the leading, vehicle will actuate the detector :cI and operate .relay Iii. It should be mentioned that in order to distinguish the references to the various controllers the preiiX I is added to the designation of any relay in the controller at intersection X and the prefix 2 tofrelay designations for the controller at intersection Z. Since relay vI RAR is operated in parallel with the lamp' R for intersectionX, yrelay I 0;- Will'belocked over armature Iara. Armaturey IoZthereupon prepares a repeat detector impulse circuit and armature E03 prepares a'ci'rcuit for relay OR in the Y controller while armature |04 (see vo4 in Fig. l) operates the phase A road relay IE in the Xeontroller. yRelay IE locks up in the manner previously described and prepares to change the right of way from'phase B to phase A'when a suitable gap in the phase Btrailic occurs or at the end of the phase B maximum period.

When the X controller subsequently steps to position fl, the amber lamps for both phases will be lightedr the phase A red lamp remaining alight and consequently the block of traffic will prepare to commence movement. Relay IAAR will now be operated in parallel with .the phase A amber lamp and consequently at armatures ladri and I mm2 circuits will be completed to the controller at intersection Y.

Armature laarl completes the repeat detector impulse circuit which extends a loop across terminals Q and R and thereupon operates relay E in the Y controller and thus prepares this controller in advance of the block of trailic at X approaching Y. When thev controller at intersection X subsequently changes over to positions 5 and 6 giving right of way to phase A tramo, relays EAAR and ERAR will be released and further vehicles passing over the detector :L'I will impulse relay il? which thereupon puts in calls at 1 both the X controller and also the Y controller 'over the back .contacts of these relays. This red-amber period caters for a condition where for example there are only such a small number of vehicles waitingatintersection X that they can be accommodated between the detector :rl and the stop line at the intersection. If this arrangement were not made, when they received right off way no repeat impulse would be transmitted to the succeeding intersection unless a further vehicle passed over detector xl and the traiiic might therefore be held up at intersection Y.

A Armature laarz completes an operating circuit for relay OR in the Y controller and thereupon this relay locks by Way of armatures orI and m'fi, and at armature orz, Fig. 1, a circuit iscomv pleted by way of a suitable tapping on resistancev switch J between terminals I 0 and I I is open shown in Fig. l after the lapse of the predetermined interval the lamp FC will strike and thus operate relay C at the same time as the rst vehicle of the block of traiiic should reachthe detect yi.. Should the Y controller not be shcw ing green to the main road,I either relay or both relays RAR and AAR will be operated in parallel with the associated phase A signal lamps and there will thus be no circuit for relay M as rar 5 or curb or both will open but a circuit will be completed for relay MR by way of solenoid contaets S3 and armature c2. Armature mri, Fig.` 2, reupon opens the locking circuit of relay OR iff/Lich releases and at armature orzopens the locking circuit of relay C which was previously vheldb'y wayf'of larmatures `cl and 0T2, switch rEl and'resistance CR, while armature 073 shunts way in the normal course; Athe waiting period isv reduced to a minimum however since a repeated detector impulse will already have been store'd when right of way was taken from the main road.

In case however the Y controller is showing green to the main road at the conclusion of the phase displacement timing period, relay C upon operating f' will operate relay M in addition to relay MR andthis relay will lock up by way of armatures TM5, aar, 'mi and solenoid contacts S3. Armature c3 discharges condenser QB over resistance YB and contacts Clt and when relay C is subsequently released as described before, relay M remains locked and at armature m2 vcompletes the phase A maximum timing circuit by way of the adjusting switch MA and a suitable tapping on resistance BR. This maximum timing period has therefore been started a predetermined interval'after the traiiic was released from intersection X. l

Though the method of interlinking between two intersections has now been described in dee tail it will be desirablev to consider the threeintersections as a Whole in order to appreciate fully the working of this system. Considering the main road which .is shown in Fig. 3, it will be realized that in the absence of cross traffic and after the passage of a vehicle along the main road the controllers at each intersection will be showing green to the main road. Under this condition there is no maximum interlinking since the interlinking pulses are sent only on red-amber and it will be understood that this arrangement is satisfactory since if there is waiting cross traffic the repeat detector impulsing facility will maintain right of Away for the main road until suitable gaps occur in the main road traflic. Should right of way be taken away from the main road at one or more intersections and the main road traffic become so'heavy as to be substantially continuous, the traiiiic will in effect be divided into"blocks' the size of which is dependent on the speed of the traffic and the length of the maximum yperiod at any controller. These blocks will be passed forward to each intersection in turn where the maximum period is arranged to commence when the leading vehicle of the block reaches the intersection and where the maximum period terminates when the last vehicle of the block has passed through.

The eiect of the maximum interlinking in producing progressive movement through the series of intersectionsv is illustrated in Fig. 4 which shows a distance time diagram of progressive traic movement through the intersections X, Y, and Z as provided by the interlinking under maximum traffic conditions. The Fig. 4 diagram assumes the intersections X, Y and Z to be 1000 ft. apart and also assumes a steady speed of traflic at 40 ft. per second or about 27 miles per hour. The diagram also assumes that the maximum time settings of adjustment switches NA yand MB in the several controllers at X, Yl and Z are all set uniformly to provide about 22 seconds of green, 3 seconds of amber, and 25 seconds of red on each street. The adjustment switches PDI and PD2 under, these circumstances may be ing of displacement period fon Y in similar yfashion to the illustration shownfor eastbound set, for'example, to provide a displacement time period of about 28 seconds as timed by condenser QC, which is about equal to the time required for a vehicle to travel from the detector :ci at the t X intersection to the Y intersection.

It will be noted in this distance time diagram that trailic proceeding eastbound thro-ugh intersections X, Y, and Z in series is illustrated as proceeding diagonally upward to the right, and

westbound traine is illustrated as proceeding dif-5l agonally downward to the right. Thev position of a block of eastbound vehicles is illustrated along a time line t taken for example at about 47 seconds on the time scale. The block of vehi-wffr cles approaching intersection X appears as atl-'5 series of short heavy Vertical lines, and it will be noted that the leading vehicle in the block illustrated as having just passed over detector :nl at vabout the beginning of the amber periodrx`y` of the cross road at intersection X. Above thisv`20 point along line t the arrow indicates the transmission of an impulse to relay OR at intersection Y to start the timing of the displacement period by charging of condenser QC. The dis-,frv

to about 75 seconds at which point the green signal will have justbeen returned to the main road at Y, assuming that the' cross road green signal was held to a maximum. The maximum@ I main road green period is illustrated as starting: at termination of the displacement period and extending to about 97 seconds where the amber signal would'be displayed.

placement period at Y extends toward the right 5 The diagram of Fig. 4 shows the main road red periods as heavy horizontal lines, and the main road green (and amber) periods appear as the spaces along the intersection lines be. tween the heavy horizontal lines. It will be appreciated that all these time periods appearingm 40 trai-o. If impulses were received from both Z and X then the displacement period would be timed as described above in accordance with the shortest time setting `for the charging vof con-;

denser GC. In the present'instance since they speed of traffic is assumed the same in opposite directions and the maximum traino conditions are illustrated the displacement period at Y would be initiated simultaneously by eastboundnu' the diagram.l

c5 started thefdisplacement period as illustrated in If the cross trac were to decrease so as to require a minimum of l2 seconds `at intersection Y alone for example the main red period just to Y"zo the right of the line t in Fig. 4 would terminate earlier atI about 62 seconds. Except for eastbound vehicles which vmay have turned into the main road at intersection X or westbound vehicles which may have turned into the main road .75

AInail). road.

ensayar proceedingabove the assumed speed, this early' termination of the main road red signal at Y will have noeiiect on the movement of eastbound traic, since eastbound trafc proceeding at normal speed would arrive at about 75 seconds. The early termination will, of course, assist in clearing the vehicles which may have turned'into the If tranic conditions changed so that the cross road traiiic at all the intersections decreased and required a minimum period of only about l2 seconds for example the resultingshortening of the main road red period would allow main road traine to start earlier at each of the intersections and with the same maximum and same displacement based' on the same tralc speed, the effect would be to shorten the total signal cycle. A single vehicle turning into the main road at intersection X and proceeding eastbound will have no iniiuence on the maximum interlinking between X andfY, but such vehicle may have an eiect in the maximum interlinking between Y and Z. ASuch effect by a turning vehicle, however, is limited since if such vehicle actuates the detector yl' inthe main road red period ahead of the leading vehicle in the block of vehicles approaching from 'X the transmission of the interlinking impulse to relay ZEJR at Z will be delayed until cross road amberperiod at Y, which is substantially at the end of the main period at Y. If the cross road trac at Y yholds the main red to a maximum the effect of the turning vehicle 'will be the same as if the leading vehicle lin the regular block of traffic 'actuated detectoryi. If, however, the main red at Y terminated before its maximum then the turning vehicle would to that extent start the displacement period at Z sooner and the subsequent maximum main green at Z would occur sooner. Generally with such shorter main road red period at intersection Y the mainred period at 'the other intersections will also be shorter due to generally lighter cross vtraicv so that suchl turning vehicles would not have' much eiect on the system as a continuing matter at an ordinary series of intersections.

It will be appreciated that in many instances in applying the maximum interlinking feature of the invention to expedite ythe movement of through traffic along the main road, the addition of the repeat pulsing feature will be of. considerable advantage, since as described, this feature will provide that actuations of eastbound trafc at intersection X are also transmitted to lintersectiony Y4 sb as to present a demand for'v subsequent transfer of the `green signal tothe main road at Y if it has been onthe cross road and will also tend to maintain the green signal on the main road at Y by resetting of the charge on condenser QA at Y if the greensignal is already on the main road in the vehicle interval position of the Y controller.

It will be seen that this method of progressively co-ordin'atlng a series of traino-actuated controll 1ers by providing a predetermined displacement period before commencing the maximum timing at each intersection enables heavy main road tran-lc to proceed without undue delay whilst at.

the same time sufficient time is allowed to enable cross traffic to lter through. There is no master controller to involve the possibility of interference during light traiic periods .and furthermore inv place of the arbitrary termination of right of way periods by a master controller during'periods of heavy trahie the system described provides, a related sequence of commencement of`maximum periods at successive',intersections which is nexiblein'accordance with the varying traido conditions. 1

Referring again to Fig. l it will be seen that when the switchJ' between terminals iii and Il is closed, relay lVi will be operatedjno matter which signal lamps are'lit at the time Ofcompletion of phase displacement timing. A pulse will therefore be stored should the lamps not be showing greenv to the main road at the completion of'displacement timing'and this arrangeing the controller more quickly into,

Two phase displacement switches vPDI and PD2 are'provided in each controller to cater4 fory vehicles approaching from opposite directions and it will be understood'that in the event of relays OR and PR being operated simultaneously by traffic which is vbeing freed from the adjacent intersections, the rtime interval represented by the switch with tlielowest resistance setting will become eective. y

j in order to' prevent right of' way being Withheld from tiiejcross roads during light traliic v periods if for example `a main roadfdetector pad should beccrne permanently operated and there are no other'vehicles in' the main road to give anv interlinked maximum 'from an adjacent intersection, a long maximum charging circuit is provided by way of 'resistance BR 4and resting armature m2. y, I

We claim: ,j i

l. In a traic'control system for a' plurality of intersections .of cross roads with a'common main roaduhaving' at each intersection rightof Way signalling means for the main and cross roads, trafi'lc actuated means in each road, va time-controlled mechanism for operating said signalling soY means to transfer accord of right ofway alternately to the roads in response to actuation of 1 the traffic actuated means in the respective roads and to prolong right of way in a road where it is being accorded upon further actuation of the tranic actuated; means in such road, a maximum timer associated with said mechanism for limiting such prolongation of right of way on the main road at one intersection when initiated in operation, and means operated by actuation of the trame actuated means in the main road at another intersection by trail-lc thereat approach- Ling said one intersection to initiate operationfof the maximum timer at said one intersection subsequently during accord of right of` Way to the main road at said one intersection.

2. In a traffic control system for a plurality of intersections of cross roads with a common main road having at each intersection right of way signalling means for the main and Vcross roads, traic'actuated means in each road and timecontrolled mechanism for operating said signalling means 4to transfer accord of right of Way alternately to the roads in response tov actuation of the traiiic actuated means in the respective roads andy to prolong right of way ina road Where vit i's being accorded upon further actuation of the tramo actuated means in such road', a maximum timer .associated with said mechanism for limiting such prolongation of right 0f Way on of Way so accorded to the respective roads for a intersection, and means operated by said timing-v A the main road at one intersection when initiated in operation, and means operated by actuation of the traffic actuated means in the main roadv at another intersection by traic thereat approaching said one intersection to initiate operation of the maximum timer at said one intersection atthe end of a time period after such last named actuation, Which period is substantially equivalent to the expected time of travel `of traflic from said other intersection to said one intersection.

3.` In a traiiic control system for a plurality of mechanism at each of the intersections each nately to themain and cross roads at the intersections in response to actuation by traic in the respective' roads and including minimum; and maximum time limiting devices to maintain right minimum period and up to a maximum period,

the main road in passing another of said intere the latter in case of a plurality of successive trafc actuations; means actuated by the iirst unit of tramo approaching one of the intersections along sections While right of Way is accorded to the main road at said another intersection, and means associated with the mechanism at said one intersection to measure a time period beginning With and in response to such actuation ofthe `last named trafc actuated means and of predetermined length substantially equivalent 'to the time required for such actuating traic to travel between said intersections and operating at the end of suchv travel time 4period to reset the maximum time device at the latter intersection on the main road if right of' Way is accorded to the main road, to measure a maximum time limit from such end of such travel time period Whereby traffic proceeding along the main road from said another intersection to said latter intersection may be given a maximum right of Way period at said latter intersection starting substantially With the arrival of the `first unit of traflic at said latter intersection.

4. In atraiiic control system for a plurality of intersections of cross roads With a common main road having at each intersection right of Way signalling'means for the main and cross roads, tramo actuated means in each road, and time vcontrolled mechanism for operating said signalling means to transfer accord of right of Way to one of the roads in response to actuation of a trac actuated means occurring therein While right of Way is not accorded in such road l further timing means initiated into operation substantially when right of Way is rst accorded to the main road at an adjacent intersection and in response to` actuation of the traffic actuated means inthe main road thereat by traffic approaching said one intersection, for timing a period of predetermined length which is substantially the time required for a vehicle on the main road starting through said adjacent intersection toward said one intersection to reach said one initiated by cross road'traic actuation.

5. In a traii'ic control system for a plurality*I of intersections of crossroads with a common main road having at each intersection right of roads, tramo actuated means in each road, vand time controlled mechanism for operating ,said

of a tralic `actuated means occurring therein While right of Way is not accorded in. such road and to prolong right of Way by actuation of the traine actuated means occurring While right of `Way is accorded to said one road; a maximum timer associated With said mechanism` at one intersection and having a long time period `for limiting such prolongation of right'of Way on the main road, further timing means initiated into operation substantially when right of Way is first accorded to the main road at an adjacent intersection and in response to actuation of the traffic actuated means in the main road thereat by trafc approaching said one intersection, for timing a period of predetermined length which is substantially the time required for a vehicle on the main road starting through said adjacent intersection toward said one intersection to reach said one intersection, meansoperated by said timing means at the end of the last named period While right of Way is being 'accorded to the main road road having at each intersection right of way signalling means for the main and cross roads,

traine actuated means in each road, and timecontrolled mechanism for operating said signalling means to transfer accord of right of way lto one of the roads in response to actuation of a traffic actuated meansoccurring therein While `right of way is not accorded in such roadand to prolong right of Way by actuation of the traiic actuated means occurring While right of Way is accorded to said one road; a maximumtimer.

associated with said mechanism at one interl `means at the end of the last-named period to" render said maximum timer effective to be so Way signalling means for the main and cross',

l0 Asignalling means to transfer accord of right of d `Way to one of the roads in response to actuationl at said one intersection to reset said maximum timer to restart it for timing a shorter maximum section for limiting such prolongation ofright of Wayon the main road, means operated by said mechanism at another intersection upon transfer of right of Way thereat to the main road in response to actuation of the traffic actuated means in the main road by traffic approaching said one intersection to cause subsequent initiation of timing by the maximum timer at said one intersection.

7. In a traflic control system for a plurality of intersections of cross roads with a common main road having at each intersection right of Way signalling means ior the main and' cross roads, traic actuated means in each road, and .timecontrolled mechanism for operating said signalling means to transfer accord of right of way to one of the roads in response to actuation of a traiiic actuated means occurring therein while right of way is not accorded in such road and to prolong right of way by actuation of the traffic actuated means occurring While right of Way is accorded to said one road; a maximum timer associated with said mechanism at one intersection and having a longtime period for limiting such prolongation of right of way on the main road-and'initiated'into operation by actuation of' the cross roadL traffic actuated means While right of Way is accorded lto said main road,timing means at said one intersection, initiated into operation substantially When right of Way is rst accorded to the main road at an adjacent intersection and in response tov actuation of the traffic actuated means in the main road thereat by traflic approaching said one intersection, for timing a period of predetermined length which is substantially the time required for a Vehicle on the main road starting through said adjacent intersection toward said one intersection to reach said one intersection, means operated by said timing means at theend of the last-namedvperiod While right of Way is being accorded to the main road at said one intersection if the maximum timer tnei'eat has been so initiated into operation to reset saidmaximum timer to restart it for ,timing a shorter maximum` period.

8. ln a traflic control system for a plurality of intersections of cross roads With a common main `road Aharing at each intersection right of Way signalling means for the 1main andcross roads,

traidoA `actuated means in each road, and timecontrolled mechanism for operatingsaid signalling means to Vtransfer accord of right of Way to one of the roads for a time. period in response tov actuation or" a traflic actuated means occurring l therein while right oi `Way is not accorded in suchintersection and havinga long time period for limiting such prolongation of` rightof Way on the main road andiinitiated into operation by actuation of the vcross lroad traffic actuated means,A

While rightI of vWay is accorded to said main road,

,timing means, initiated into operation substantially When right of Way is first accorded` tothe main road at an adjacent intersection and in response to actuation of the traiiic actuated means inthe main road thereat by traffic approaching said one intersection, for timing. a period of predetermined length which is substantially the time required for a vehicle on the main road starting through said adjacent intersection toward said one intersection to reach said one intersection, means operated at the end of the last-named. period While right of Way is beingaccorded to the cross road at said one intersection to reduce the time period of ,saidmaximum timer to a Value considerably less than said Ylong time period when said maximum timer neXt operates during following accord of right of Way to the main road, said last named means comprising relay means connected to be initially energized by said timing means at the end of its timing period, a locking device for said relay means i,

to maintain it energized rafter such initial ener,-

4 gization a control connection between said locking device and said mechanism at said one intersection to release said locking device only momentarily at the end of the main road right of way period, anda timing control circuitmeans for said timing means connected with saidr relay' means to be operated by energization of the latter to reduce the timing period of said timing means.

9. vIn a traic control system for a plurality of ling means to transfer accord of right of Way toone of the roads in response to actuation of a traflic .actuated means occurring therein While right of Way is not accorded in such road and to prolong right of Way by actuation of the traic actuated means occurring While right of way is accorded to said one road; amaximum timer associated With said mechanism at one intersection for limiting such prolongation of right of way on the main road and initiated into operation by actuation of the cross road -trafc actuated means While right of Way is accorded to said main road, timing means, initiated into operation substantially When right of Way is first accorded to the main road at an adjacent intersection and in response to actuation of the trafilc actuated means in the main road thereat by traiiic approaching said one intersection, for timing a period of predetermined length which is substantially the time required for a Vehicle on the main roadstarting through said adjacent intersection tov/ard said one intersection to reach said one intersection, means operated at the end of the period of the last-named means if right of Way is being accorded to the main road and said` maximum timer has been so initiated at said one, intersection to reset said maximum timer substantially toI zero whereby a group of Vehicles released at said adjacent intersection are ensured right of Way at said one intersection without interruption by said maximum timer.

10. In a trac control system for a plurality of intersections of `cross roads with a common main roadhaving at each intersection right oi Way signalling means for the main and cross roads, tramo actuated means in each road, and timecontrolled mechanism for operating said signal- .ling means to transfer accord oi rightI of way to one of the roads in response to actuation of a traic vractuated means occurring therein While right of Way is not accorded in such road and to prolong right of Way by actuation ofy the traffic actuated means occurring while right ofway is accorded to said one road; a maximum timer associated with said mechanism at one intersection and having a condenser, means including resistance for'charging said condenser at a slow rate When connected to said condenser, means responsive to a predetermined value of charge on said condenser to cause transfer of right of Way from the main road to the cross road, means operated While right of way is on the main road upon actuation Aoi the trailic actuated means lin the cross road to connect said charging means to said condenser, further timing means, initiated into operation-when the signalling means at an i adjacent intersection transfers rightrof way to the main road in response to actuation oi the vtralic actuated means in the main road by trafiic approaching said ,one intersection, for timing a period of predetermined length Which is substantially the time required for a Vehicle on the main roadv to travel from said adjacent intersection to said one intersection, and means operated at the end of the period of said last-named means to dis-charge the condenser of the maximum timer momentarily in order to prolong the maximum time period of right of Way on said main road.

l1. In a traiiic control system for a pluralityof intersections of crosstrac lanes With a common 'main lane rhaving at each Aintersection traffic actuated means in the lanes, traiiic signal control rnechanism for displaying go and stop Isignals alternatelyA to each lane inv acycle for time periods in accordancewith actuationof the v trac actuated means in the respective lanes,

means including a timer at one intersection and operating when effective to limit the go signal period on the main lanethereat within a maxi- 1 mum time period, a first relay operated by actuation of the traino actuated means in the main lane at another intersection, a second relay operated in each cycle by said mechanism at said other intersection during the time period said signal, a stick circuit for said rst relay including 'v ing circuit to the control mechanism at said one a make contact of said second relay, an impulsintersection and including a make contact on said first relay and make contacts on said second and third relays in series whereby operation F of said iirst relay during said portion of the stop signal period completes said impulsing' circuit immediately to said control mechanism at said one intersection and operation of said yfirst relay during any other portion of the cycle r prepares said circuit for completion only by said second and third relays when said portion of the stop signal period is reached, and means re- `sponsive to completion of said impulse circuit to render said timing means so effective to limit the next subsequent go signal period on the main lane at said one intersection.

12. In a trafc control system for-a plurality of intersections of cross roads with a common main road having at each intersection right of way signalling means for the main andrcross roads, trai-'o actuated means in each road, and timecontrolled mechanism for operating said signalling meansto transfer accord of right of way alternately to the roads in response to actuation `of the traffic actuated means in the respective roads and to prolong right of way in a road where it is being accorded upon `further actuation of the traffic actuated means in such road, a maxi- `mum timer associated with said mechanism for :limiting such prolongation of right of way on the main road at one intersection when operating, a time controlled switch means having switch means operated at the end of a time interval from energization, contact mea-ns operated by actu-y ation of the traffic actuated means in the main road at another intersection by traffic approach- `ing said one intersection, means including said contact means to energize said time controlled switch means, contact means operated by the said mechanism of said one intersection during accord of right of way to the main road thereat, contact means operated by the` tramo actuated means in the cross road at the latter intersection and circuit means connecting the two last ynamed contact means and said switch means to so operate said maximum timer responsive to said two last contact means and said switchmeans being operated..

13. In a traino control system for a plurality of intersections of cross roads with a common main road having at each intersection right of way signalling means for the main and cross roads, tramo actuated means in each road, and timecontrolled mechanism for operating said signalthe traffic actuated means in such road, a maxiv mum: timer-associatedwith said-mechanism for' g limiting such prolongation of right of way on.

the main road at'one intersection when operating, a time controlled switch means having switch means operated at the end of a time interval from energization, contact means operated by actuation of the traffic actuated means in the main road at another intersection by traflic appreaching said one intersection, a second contact means operated by the said mechanism of said other intersection substantially upon transfer of right of way from the cross road to the main road thereat, means including the first and second contact means to energize said time controlled switch means, contact means operated by i the said mechanism of said one intersection during accord of right of way to the main road thereat, contact means operated by the traic actuated means in the cross road at the latter vintersection and circuit means connecting'fthe two last named contact means and said switch means to so operate said maximum timer responsiveV to said two last contact means and saidv switch means being operated. f

14. In a ,trafic control system for a plurality of intersections of cross roads with a common main road having at each intersection right of way signalling means for the main and cross roads, tramo actuated means in each road, and timecontrolled mechanism for operating said signalling means to transfer accord of' right of way alternately to the roads in response to actuation of the traine actuated means in the respective `roads and to prolong right of way in aroad where it is being accorded upon vfurther actuation of the tranic actuated means in such road, a

by actuation of the trafiio actuated means in the second contact means to energize said time controlled switch means, contact means operated by the said mechanism of said one intersection durmg accord of right of way to the main road thereat, contact means operated by the traffic actuatedmeans inthe cross road at the latter intersection and.l circuit means connecting the maximum timer associated withv said mechanism `for limiting such prolongation of right ofway` on the main road at one intersection when'` operating, a time controlled switch means having switch means operated at the end vof a time interval from energization, contact means operated two last named contact means and said switch means to so operate said maximum timer, responsive to said two last contact means and said switch means being operated, and said time controlled rswitch means having its time interval adjusted to be substantially equivalent to the expected time of travel of traflic from said other intersection to said one'intersection.

15. In a traic control system for 'a plurality of intersections of cross roads with a common main road having at each intersection right of vWay signalling means for the main and cross roads; l

tramo actuated means in each road, and time controlled mechanism for" operating said signalling means to transfer accord of right of Way alternately to the roads in response to actuation of the trame actuated means in the respective roads and to prolong right of Way in a roadA where it vis being accorded uponv further `actuation of the trac actuated means in such road,

ya maximum timer associated with said mechanism for limiting such prolongation of right of way on the main road at one intersection when operating, a time controlled switch means having switch means operated at the end of a time interVal from energization, contact means operated by actuation of the trac actuated means in the main road at another intersection by traic approaching said one intersection, a second contact means operated by the said mechanism of said other intersection substantially upon transfer of right of way from the cross road to the main road thereat, `means including the first and second contact means. to energize said time controlled switch means, contact'means operated by the said mechanism of said one intersection during accord of rightrof way to the main road thereat, contact means operated by the traffic actuated means in the cross road at the latter intersection and circuit means connecting the two last named contact means and said switch means to so operate said maximum timer, re-

sponsive to said two last contact means andsaid switch means being operated, said switch means comprising a switch operated momentarily at the end of the time interval of said time controlled switch means, a relay, an energizing circuit for said relay including the last named switch and further contact means closed by said mechanism during accord of right of way to the main road at said one intersection, a stick circuit for said relay including a contact means opened by said mechanism only momentarily at the end of the last mentioned accord of right of way, a switch included in said maximum, circuit means and operated by said relay when energized to prepare said circuit means to operate said maximum timer responsive to operation of the two contact means connected to said circuit means, and a switch connected to said further contact means and manually operable for shunting said further contact means.

GEORGE WILLIAM THOMPSON.. ALFRED PERCY BAILEY RENSIIAW. 

